docs: def from_update(cls, update):
          """ Factory for creating an Update expression """
          expressions = []
          if update.set_expr:
              expressions.append(UpdateSetMany.from_clause(update.set_expr))
          if update.remove_expr:
              expressions.append(UpdateRemove.from_clause(update.remove_expr))
          if update.add_expr:
              expressions.append(UpdateAdd.from_clause(update.add_expr))
          if update.delete_expr:
              expressions.append(UpdateDelete.from_clause(update.delete_expr))
          return cls(expressions)